"Once I knew that this was my reality, I decided to be proactive and to minimize the risk as much I could," she wrote. "I choose not to keep my story private because there are many women who do not know that they might be living under the shadow of cancer. It is my hope that they, too, will be able to get gene tested, and that if they have a high risk they, too, will know that they have strong options."

Other celebrities took to Twitter to applaud Jolie for her bravery.

I commend Angelina Jolie for her courage and thoughtfulness in sharing her story today regarding her mastectomy. So brave!